High performance controller with effective voltage balance regulation for a cascade STATCOM with star configuration under unbalanced conditions

A high performance controller with effective voltage balance regulation is proposed for a cascade STATtic synchronous COMpensator(STATCOM) with star configuration. Zero-sequence voltages are injected to the output voltages of STATCOM in order to compensate the unblanced load currents, which can also decouple the star-connected three-phase STATCOM system into three single-phase systems. Additionally, an effective voltage balance control method and a robust current tracking technique are proposed to guarantee all capacitor voltages balanced and to ensure good current tracking ability. Moreover, a quick and accurate current extraction method is proposed to obtain the negative and reactive currents of unblanced loads to improve the system´s dynamic response. The proposed control method is validated on a 10kV/±1Mvar cascade star-connected STATCOM industrial prototype. All the experimental results verify that with the proposed control methods the STATCOM can compensate unblanced load currents with quick dynamic response while keeping all capacitor voltages balanced.